Slicing polyacrylamide gel cylinders into discs of precise thickness has been a long-standing problem. Analysis of gel bands is limited by the precision with which the slices can be cut. There is a considerable literature of various devices which have been proposed, but the problem had evaded satisfactory solution. In general, the devices reported in papers or produced commercially fall into two classes: those using the egg slicer approach, in which multiple blades or wires cut across the gel plug simultaneously: or else systems which regularly advance the gel into the path of a very sharp blade moving across the gel.
The patent to Johnson, U.S. Pat. No. 3,450,333 and the patent to Mills, U.S. Pat. No. 3,759,127, both disclose apparatus for the cutting of thin wall cylinders, a non-analogous work product, wherein a plurality of cutting blades are placed to contact with the outer surface of the cylinder and moved radially inwardly during the cutting process. In both of these patents the cutting surface is shown to be a plurality of cutting wheels. In the Johnson patent the tube is rotated as the cutting wheels move inwardly thus applying an approximately equal amount of force around the circumference of the tube and avoiding substantial deformation thereof during the cutting process. In the Mills patent the cutting blades are moved inwardly until their edges touch thereby shearing off the desired length of tube by cutting it all about its circumference.
Neither of these patents, however, discloses the application of the substantially identical cutting force around the entire circumference of the cylinder to be cut. Neither of these two devices disclosed in the patents to Johnson and Mills would be suitable in the environment of the present invention because the use of apparatus similar to those shown in the patents to Mills and Johnson would result in the same deformation problems discussed below with regard to prior art devices which have been used to cut gels into discs.
Other ideas which have been considered for cutting gels are the use of curved blades, rotating blades, moving wires or saw-toothed blades, and the use of freezing to stiffen the gel. Some methods achieve success (defined as a precision of better than 10% relative standard deviation of slice thickness or weight) on some gel formations, but are not universally applicable to any size or consistency of gel.